THE manager of the secure unit housing some of Britain's most dangerous juvenile delinquents last night fiercely criticised the policy of putting youngsters behind bars.

Gill Palin manages the Aycliffe Secure Unit in County Durham - the children's centre that once claimed to be "the last resort" for Britain's most difficult youngsters.

Over the years Aycliffe has garnered an international reputation for its work with troubled children. It has housed some of the most notorious young people in Britain, including, murderers, rapists and arsonists.

However, Mrs Palin said she despaired at the number of children being locked up - and said there were young people in her care who should never have been imprisoned.

"A society is judged by how it treats the most vulnerable people in society, and the children who come here are vulnerable," she said. "It is damning for us as a society to lock some of these children up."

Her comments came on the eve of a report saying the policy of jailing child offenders is prohibitively expensive.

Crime reduction charity Nacro says the problems of child offenders were made "significantly worse" by locking them up. The report out today, Counting the Cost: Reducing Child Imprisonment, criticises the Government's use of child detention as "damaging and counterproductive".

Harsh punishments such as jail may make young people up to a quarter more likely to reoffend, the study claims.

Imprisonment of under-18s in England and Wales rocketed by 90 per cent from 4,000 in 1992 to 7,600 in 2001.

During the same period the number of under-15s who were locked up rose by 800 per cent, says Nacro.

"Reoffending rates for young offender institutions are as high as 84 per cent, with a six-month custodial sentence costing the taxpayer an average of £21,000," it says.

"By comparison, alternative non-custodial options for a similar six-month period cost as little as £6,000 and have markedly lower rates of reoffending."

Although Aycliffe is not classed as a young offenders institution, it does have a secure unit. Mrs Palin said a knee-jerk reaction to high profile offenders had seen a steep increase in the number of custodial sentences.

"Some children do need to be locked up because of the risk they represent, but for some children there are better alternatives," said Mrs Palin.

"Locking children up does not work. You can forget about them for a while, but they come back to haunt you again and again. If we got more money into preventative services, then fewer children would come into the custody arena."

A Home Office spokesman said they could not comment on sentencing policy. "It is for the judges to sentence, not for the Home Office," he said.

But Claire McCarthy, of prison campaign group the Howard League, said judges had come under increasing pressure to hand out tougher sentences to young offenders.

"Any child that gets into trouble is demonised and called evil, and we feel that affects sentences," she said.

In an interview with The Northern Echo in 1999, Tony Blair said if young people were a menace to the community they should be locked up.

And a central plank in last year's Queen's Speech was a crackdown on so-called yob culture.

But Ms McCarthy said high reoffending rates proved that custody was ineffective at cutting crime.